The long range goal of this study is to understand how the positions of cell cleavage planes are specified. The orientation and asymmetry of cell division are established by the angular and axial position of the mitotic spindle respectively, and similar mechanisms which align the spindle have been demonstrated in diverse organisms. Cleavage plane specification is likely to be essential to the process of cellular differentiation and thus relevant to diseases such as cancer in which this process is perturbed. The mechanism of spindle alignment will be studied in the Caenorhabditis elegans embryo where it is amenable to genetic analysis, and where a stereotypic pattern or oriented and asymmetric cell divisions takes place. A novel strategy will be employed to isolate mutations which disrupt the normal pattern of embryonic cell divisions. In addition, potentially interesting embryonic-lethal mutants from existing collections will be screened for cleavage-pattern irregularities. Once obtained, mutants will be analyzed for defects in the alignment mechanism by following the movement of centrosomes during the early divisions using multiple-focal-plane time-lapse video microscopy, and by determining the distribution and behavior of cytoskeletal elements and associated proteins implicated in this process using fluorescent imaging techniques. Also, the impact of these mutations on the segregation of cytoplasmic factors and the production of cell-type specific markers will be determined. The isolation and analysis of mutations that affect cleavage plane specification will be an important step in elucidating the mechanism of this important process.